The present invention relates to a green ceramic body, in particular a green ceramic film having a photostructurable function layer containing platinum and a method of producing such a green ceramic body.
The Fodel technology developed by DuPont is already known for producing structured resistance layers or printed conductors on green ceramic bodies, which are designed in a zigzag or meandering pattern, for example, in some areas.
In particular, a paste is printed onto green ceramic films and subsequently structured by using a photomask and exposing with UV rays. This structuring is then followed by developing the paste in the exposed areas. However, a disadvantage of this technology is that a yellow room is always necessary because the pastes are sensitive to daylight. In addition, the known pastes based on the Fodel technology are suitable only for maximum temperatures of 900xc2x0 C., i.e., the green ceramic films to which the structured pastes have been applied can then be fired or sintered at max. 900xc2x0 C. However, these temperatures are often not sufficient Moreover, it is not possible with the Fodel technology to simultaneously produce coarse and very fine structuring on the green films. Finally, such pastes have only a limited suitability for producing function layers containing platinum and they are often sensitive to oxygen.
In addition, it is also known that pastes containing platinum can be applied instead of green ceramic films to ceramic substrates which have already been fired and which can then be provided with structured function layers by photostructuring. This method permits fine structuring down to a lateral dimension of approx. 10 xcexcm, while only structures having a lateral extent greater than 100 xcexcm can be produced by the traditional screen printing technology.
German Published Patent Application No. 199 34 109 describes the manufacture of a temperature sensor, where meandering printed conductors or resistor paths of platinum are first printed on green ceramic films, then are built up in the form of a multilayer hybrid using additional green ceramic films and next are sintered to form a temperature sensor by the cofiring technology. However, only printed conductor widths and spacings of approx. 0.2 mm can be achieved because of the thick film technology used here.
Due to the fact that known photostructurable function layers containing platinum can be applied only to prefired ceramics and can be processed only with a very complicated process technology (nitrogen atmosphere, yellow room, etc.), they cannot be integrated into existing manufacturing methods.
In this regard, Lithuanian Published Patent Application No. 97 161 has already described a photostructurable paste containing platinum which is suitable for application to prefired ceramic films and can be structured by photostructuring after application to form a function layer containing platinum. The typical lateral structure resolution is 10 xcexcm to 30 xcexcm.
The object of the present invention was to modify the photostructurable paste described in Lithuanian Published Patent Application No. 97 161 so that it is also suitable for direct application to green ceramic films and thus for producing a green ceramic body having a photostructurable function layer containing platinum that can be processed without any great process technological complexity. At the sane time, the object of the present invention is to permit a definite increase in the structural resolution of the function layer while at the same time retaining the cofiring technology for production of multilayer structures and multilayer hybrids. This should permit the simplest possible integration into existing production lines.
The green ceramic body according to the present invention and the method according to the present invention for producing a green ceramic body has the advantage in comparison with the related art that green ceramic films can be provided directly with photostructurable function layers containing platinum in this way. These function layers can also be structured by photostructuring in the form of printed conductors or resistor paths in particular, yielding a lateral resolution of less than 15 xcexcm, in particular between 5 xcexcm and 25 xcexcm, in the resulting structures of the function layer.
In addition to a high absolute lateral resolution of the structures created in the photostructured function layers, the green ceramic body according to the present invention has the advantage that photostructuring can be performed in daylight and in the presence of oxygen. Thus, the green ceramic body and the method of producing same can easily be integrated into existing manufacturing processes, yielding significant cost advantages in comparison with known methods involving much more complex technologies.
It is also advantageous that the structures remaining on the green ceramic body after photostructuring of the function layer have only a low standard deviation from a given specified value in the lateral extent of the resulting structures in at least one dimension. To this extent, structures wider than 50 xcexcm can also be created, but they would then have a very precisely defined width, for example. The standard deviation from the specified value is preferably less than 10 xcexcm, in particular less than 5 xcexcm.
The green ceramic body according to the present invention is suitable for producing multilayer ceramic-based structures in an advantageous manner, the green ceramic body having the applied photostructured function layers also being processable to hybrid components. In addition, it is also readily possible to provide the green ceramic body with recesses and/or plated-through holes or superficial contact areas before or after applying the function layer.
Finally, the green ceramic body according to the present invention also makes it possible to manufacture the temperature sensor known from German Published Patent Application No. 199 34 109 having improved properties with regard to the resistor paths produced in this way. Furthermore, the function layer applied is very stable over time despite the addition of platinum, which has a very high catalytic activity.
For example, instead of pure platinum powder, a mixture of platinum powder with aluminum oxide powder and/or zirconium dioxide powder is also suitable as a filler in the paste applied to the green ceramic body in the form of a function layer. This mixture results in improved adhesion of the resulting function layers containing platinum to the starting green ceramic body or the starting green ceramic film (xe2x80x9cgreen tapexe2x80x9d) and/or it increases the electric resistance of the printed conductors structured in the function layer after photostructuring due to the mixture of platinum and aluminum oxide powder particles.
It is also advantageous that the photostructurable paste applied to the starting green ceramic body can be developed by an aqueous solution.
Thus, on the whole this yields a greatly improved resolution in the resulting structures of the function layer, and the ceramic substrates fired after conclusion of sintering of the green body may have resistor paths in a meandering structure, for example, having an increase in resistance of more than 400% in comparison with comparable resistor paths produced by the traditional thick film technology. Such resistor paths mean a much smaller area required with a much better accuracy of the temperature measurement and a higher measurement resistance, i.e., a better accuracy in analysis of the measurement voltage when used in temperature sensors or beating elements.
Because of the increased resolution in photostructuring of the function layer, the fluctuations in resistance values of the resulting resistor paths are also greatly reduced, thus yielding on the whole a higher manufacturing quality, fewer rejects and smaller deviations in the resulting resistance values from a given specified value.